Priority is claimed with respect to German application No. 199 01 087.0 filed in Germany on Jan. 14, 1999, the disclosure of which is incorporated herein by reference.
The invention relates to a device for creating a spread-out fiber stream of tobacco fibers along a concave-curved guide track provided with air flow openings acting in the transport direction of the fiber stream.
A guide track of the type mentioned at the outset is part of a so-called distributor of a cigarette string machine. The guide track, together with an essentially parallel directed air flow, constitutes a so-called moving bed. Tobacco in the form of a loosened and spread-out tobacco stream is moved along close to the guide track and transferred to a suction string conveyor which forms the tobacco fibers into a tobacco string.
An object of the invention is to optimize the effectiveness, or respectively the conveying capacity, of the moving bed in respect to the energy outlay for the air flow supplied.
Moreover, it is an object to improve the guide track constituting the moving bed in respect to its construction, handling and exchangeability, or respectively installation and removal.
The above and other objects are accomplished in accordance with the invention by the provision of a device for creating a spread-out stream of tobacco fibers, comprising: a concave-curved guide track along which the fiber stream of tobacco fibers are conveyed, the guide track having a generatrix based on a uniform generating curve; and at least one air jet having an air flow opening interrupting the guide track so that air exiting the air flow jet acts in a conveyance direction of the fiber stream for spreading out the tobacco fibers.
Thus, in accordance with the invention the generatrix of the guide track, which is interrupted by the air flow openings designed as air jets, is based on a uniform generating curve.
For optimizing the conveying and spreading effect it is another aspect of the invention that the air jets terminating in the sliding surface of the guide track extend continuously over the width of the guide track.
In accordance with an advantageous embodiment, a close-lying wall flow (Coanda effect) is achieved in that the downstream wall of the air jet, in relation to the conveying direction of the fiber stream, makes a transition in the form of a continuous convex curve into the concave sliding surface of the guide track.
According to a further feature of the invention, the sliding surface of the guide track is interrupted by several air jets, which follow each other in the conveying direction of the fiber stream, which increases and complements the conveyance by the moving bed.
Preferably, the air jets are connected to a common pressure chamber.
In accordance with a preferred embodiment, the guide track is put together from individual segments, whose respectively adjoining border surfaces form nozzle walls of the air jets. In this way it is possible to design and assemble the guide track flexibly, or respectively to replace it in partial areas when it is worn, wherein an optimal orientation of sliding surface walls and air jets is always assured.
The advantageous effects of the construction of the guide track in segments are further increased by a production-specific further development, in that the guide track segments are embodied as extruded sections, whose wall sections defining the sliding surface of the guide track form an upstream and a downstream located nozzle wall, in respect to the conveying direction of the fiber stream, on two successive air jets.
The invention presents the advantage that, because of the continuous transition along the sections of the guide track which are interrupted by an air jet, the tobacco meets the air flow directly at the outlet of the air nozzle, i.e. at a location at which the air flow still has its maximum flow speed and can accelerate the tobacco fibers accordingly. In this way it is possible to operate the air supply at a low air pressure, or respectively with a respectively reduced blower output, which improves the effectiveness and the economy of the energy generation and the energy output.
Furthermore, an economical production-related advantage results from the use of individual segments, which are put together to form a guide track, whose simple exterior contours actually predestine them for being manufactured by means of the efficient extrusion process.
The invention will be explained in greater detail in what follows by means of an exemplary embodiment represented in the drawings.